1. Field of the Invention
This invention relates to rope winches and more particularly relates to a rope winch suitable for raising a rope anchor warp of typically a pleasure vessel. Such a winch includes a sheave which takes one turn, and more precisely a part turn, only of a rope thereabout as distinct to a drum winch wherein several turns are normally required or recommended to achieve grip.
2. State of the Art
Single sheave winches of various designs are known, these including an earlier design of ours and which is described in U.K. Patent 2233623, and the winches described in U.S. Pat. Nos. 3,078,074 ; 3,055,638 and 3,847,378. The winches disclosed in each of these patents includes some form of impingement means to control a rope in its travel about an associated sheave. It is in this facet that the present invention differs from any of the prior art in providing an impingement means assembled in a structural relationship with other rope guide means which is not disclosed in or comprehended by the prior art.
A fundamental problem of such single sheave winches is the achieving of appropriate frictional grip on, and thus control of, a rope. Too little grip can result in slipage and too much grip can result in wedging of the rope in the sheave and consequentially the need for stripping a rope therefrom. Achieving the desired grip in an anchor winch is a particular problem as the loads involved with the lowering and raising operational modes thereof represent essentially opposite loading requirements. That is, normally there is no load in a lowering mode and full load in a raising mode. However, such nominal operational modes or conditions do not convey the complete case as the operating dynamics or requirements can at any moment change from one mode or condition to the other.
As a first example, in a nominal raising mode, at the commencement of raising an anchor may snag and the loading on the winch greatly increase. Particularly if the anchor does not promptly come free too much grip can cause overloading of the winches prime mover and/or excessive wearing on the anchor warp. With an anchor becoming free from such circumstances and, even with an essentially clear extrication, at least for an instance, no load conditions can prevail resulting in slack developing in the warp. This can cause jamming of the warp in the winch.
As a second example, in a nominal lowering mode, while there can be said to be no load there remains a need to control the warp. Nominal no load conditions arise as little load is involved in drawing a tail of a warp into the sheave however even this load can tend to be overridden by the momentum developed by a descending anchor. This can cause run through or free running of a warp through a winch. However, if there is too little grip excessive run through or free running may result which can cause jamming; typically a tail of a warp feeding into a winch can become entangled and jam-up. Further, the momentum of a lowering anchor can change abruptly with the rise and fall of an associated vessel in say the swell of the surrounding waters. For example, with the bow of a vessel coming down off a swell the momentum generated in an associated anchor can cause the warp supporting the anchor to be drawn excessively through the winch. With such excessive run through it may be necessary to reverse the operating mode of a winch to achieve braking on the warp.
Additionally it is commercially preferable that a range of different diameter warps be operable with any particular sized winch. It is manifest that reasonable correlation between the diameter of a warp and the spacing of the jaws of a sheave is fundamental to achieving grip. Achieving the aforesaid criteria for a range of winches thus also represents a problem.
An intention of this invention is to provide a one turn or single sheave winch particularly suitable for operation with a rope anchor warp which it is envisaged will alleviate the aforesaid problems or at least provide a useful choice.